The present invention relates to a storage device used as an external storage device for a computer or the like as well as to a method of detecting a position of a head on a disk used for the same and more particularly, to a storage device for detecting a position of a magnetic head on a magnetic disk with a data region and a servo region provided thereon based on time division (xe2x80x9ctime division modexe2x80x9d) as well as to a method of detecting a position of head on a disk used for the same.
In recent years storage devices having great storage capacity are widely used. As a method of detecting a position of a magnetic head on a magnetic disk in such a storage device there is know a method of previously recording the servo patterns on the magnetic disk and detecting a position of the magnetic head thereon according to the servo patterns.
As an external storage device for a computer or the like, a storage device having a magnetic disk as a storage medium are widely used. A magnetic disk has a data region for storing therein data and a servo region for previously recording therein servo patterns for servo controls existing thereon in time division mode.
This type of storage device is substantially configured with the magnetic disk, a magnetic head closely located with respect to the magnetic disk, a servo controlling section for servo controlling so that the magnetic head positions at a target position by moving the magnetic head along the direction of radius of the disk at the time of read seek and write seek, and a read/write circuit for controlling a write and/or read operation of the magnetic disk using the magnetic head.
Herein, the magnetic head has a write core for writing data in a data region on the magnetic disk with a magnetic field generated by a current for recording fed from the read/write circuit, and a read core for magnetically detecting the data written in the data region and detecting a servo pattern recorded on the servo region.
The servo controlling section detects a position of the magnetic head on the magnetic disk according to a phase of the servo pattern detected by the read core of the magnetic head and then moves the magnetic head on the magnetic disk to a target position. More specifically, the servo controlling section servo-controls the magnetic head while receiving feedback of information for a detected position obtained from the servo pattern so that a positional error between the detected position and the target position becomes zero.
Next description is made for specific configuration of the storage device based on the conventional technology and the operations performed during detection of a position of the head on the disk with reference to FIG. 5A and FIG. 5B through FIG. 9. FIG. 5A and FIG. 5B are perspective views each showing configuration of the key section of the storage device based on the conventional technology. In FIG. 5A, the magnetic disks 1111 to 111n are n-pieces of disk-shaped recording medium for magnetically storing data therein, and are located at prespecified intervals in the axial direction in a multi-layered form. These magnetic disks 1111 to 111n are rotated and driven with high speed by a spindle motor not shown in the figure. Further, each of the magnetic disks 1111 to 111n has a data region for storing the data therein and a servo region for recording servo patterns therein respectively.
In each of the magnetic disks 1111 to 111n, each region obtained by dividing a space between the most inner region and the most outer region thereof into concentric circles with a prespecified width therebetween (track pitch) is called a track TK. When the tracks TK on the magnetic disks 1111 to 111n are extracted three-dimensionally, these tracks TK are arranged cylindrically. A set of plurality of tracks TK existing at the same distance in the radial direction from the center on the surfaces of each of the magnetic disks 1111 to 111n are called cylinders C1 to Cn (Refer to FIG. 5B).
FIG. 6 is a view showing servo regions RS on each of the magnetic disks 1111 to 111n. In the figure, the same reference numerals are assigned to the sections corresponding to those in FIG. 5A and FIG. 5B, and description thereof is omitted herein. It should be noted that FIG. 6 shows an example of servo regions RS each provided as a linear shape and also shows the cylinders C0 to C3 of the cylinders C0 to Cn to facilitate the understanding thereof.
In FIG. 6, four cylinders C0 to C3 are set as one group. Those cylinders C0 to C3 (or the tracks TK) are located adjacent to each other with boundries K, K, . . . at a track pitch TP. Herein the track pitch is 2 xcexcm. A total of three lines of servo patterns S3, S3, . . . with a phase difference of 90 degree from each other are recorded in time division mode on each of the cylinders C0 to C3.
Namely, taking the cylinder C0 as an example, three lines of servo patterns S3, S3, . . . are recorded on this cylinder C1 at a prespecified interval therebetween so as to divide one track pitch TP into m (m=3 in the example of the figure) divisions. These patterns S3, S3, . . . are magnetic patterns used for positions of the magnetic heads 1131 to 113n on the magnetic disks 1111 to 111n. Herein a servo pattern length L3 of the servo pattern S3 is set to ⅓ of the track pitch TP.
Returning back to FIG. 5A, the magnetic heads 1131 to 113n each have a read core and a write core having an extremely narrow gap, and are located adjacent to the magnetic disks 1111 to 111n respectively. Each of the magnetic heads 1131to 113n has a write core W (Refer to FIG. 7) for writing data in each of the magnetic disks 1111 to 111n with a magnetic field generated by a recording current fed when writing, and a read core R (Refer to FIG. 7) for magnetically detecting the data and the servo patterns S3 (Refer to FIG. 6) recorded on each of the magnetic disks 11111 to 1111. A number n of the magnetic heads 1131 to 113n is decided according to a number n of the magnetic disks 1111 to 111n.
Herein, on the magnetic head 1131 shown in FIG. 7, a center line Xb linking the read core R to the write core W and a tangent line Xa of the cylinder C1 where the read core R positions make an angle xcex8 of yaw. A width WR of the read core R is around xc2xd of the track pitch TP because of designing restriction, and is more specifically 0.7 xcexcm to 1.3 xcexcm. Also, since there is the angle xcex8 of yaw as described above, an effective read-core width WRxe2x80x2 with respect to the cylinder C1 becomes WRxc2x7cosxcex8.
Operations for detecting a position of a head on a disk in the storage device based on the conventional technology will be described in the following. In FIG. 5A, when a spindle motor not shown herein is driven, the magnetic heads 1131 to 113n are concurrently rotated and driven. Description centering on an operation of the magnetic head 1131 will be made hereinafter to simplify the description.
Assuming herein that the magnetic head 1131 shown in FIG. 7 positions outside the cylinder C0 and that the magnetic head 1131 is moved from the current position to a central position of the cylinder C1 shown in the same figure, the servo controlling section (not shown herein) moves the magnetic head 1131 at a ⅓-track pitch in the radius direction of the disk.
With this operation, the magnetic head 1131 is first moved so as to traverse the cylinder C0. During this movement, the servo patterns S3, S3, . . . are detected by the read core R, and the servo controlling section generates a positional error signal from the difference between a detected position signal according to a phase difference of each servo patterns S3 and a target position signal according to a target position of the magnetic head 1131.
The servo controlling section amplifies the positional error signal with a gain G0 (Refer to FIG. 9) and generates an amplified positional error signal P0. Herein, FIG. 9 is a view showing a relation between an offset rate OF of the magnetic head 1131 and a voltage V (level) of the amplified positional error signal P0. As understood from this figure, the amplified positional error signal P0 changes linearly so as to be in proportion to the offset rate OF.
Then the magnetic head 1131 shown in FIG. 7 positions at the center (track center) of the cylinder C1 as a target position, a read/write circuit feeds a recording current according to write data to the write core W of the magnetic head 1131. Thus, write data is written in the data region (not shown herein) by the write core W. Although description in the conventional type of storage device has been made for the servo patterns S3, S3, . . . obtained by dividing the track pitch TP into three lines in each servo region RS of the cylinders C0 to C2 shown in FIG. 7, there is also an example of recording servo patterns S4, S4, . . . obtained by dividing the track pitch TP into four lines as shown in FIG. 8 on the track TK.
In the example shown in FIG. 8, taking the cylinder C0 . . . (track TK) as an example, four lines of servo patterns S4, S4, . . . are recorded on this cylinder C0 at a prespecified interval therebetween so as to divide one track pitch TP into m (m=4 in the example of the same figure). A length L4 of this servo pattern S4 is set to xc2xc of the track pitch TP, so that this length is shorter than the servo pattern length L3 shown in FIG. 7. Accordingly, in the example shown in FIG. 8, the magnetic head 1131 is moved at a xc2xc track pitch TP in the radius direction of the disk.
In the conventional type of storage device as described with reference to FIG. 7 and FIG. 8, the description has been made for detection of a position of the magnetic head 1131 by using the servo patterns S3 or servo patterns S4 with the servo pattern length L3 or servo pattern length L4 as the ⅓ track pitch TP or xc2xc track pitch TP for each track TK respectively.
Herein, in the conventional type of storage device, when the servo pattern S3 with the ⅓ track pitch TP is used the magnetic head 1131 is successively fed at the ⅓ track pitch TP, and when the servo pattern S4 with the xc2xc track pitch TP is used the magnetic head 1131 is successively fed at the xc2xc track pitch TP.
It is understood from the fact described above in the conventional type of storage device that, when a length of a servo pattern is shorter, the magnetic head 1131 is moved in smaller steps which increases a time for STW (servo track writing) . Therefore, there has been a request for reducing the time for STW by making the length of the servo pattern as long as possible. This type of request is, especially in the manufacturing field of the storage device, related to reduction of facilities or the like by reducing the time for STW.
Therefore, in the conventional type of storage device, the request can be responded to by a method of using servo patterns S2, S2 each having a servo pattern length L2 of xc2xd of the track pitch TP for each track TK as shown in FIG. 10. Namely, when the method described above is used, as the servo pattern length L2 of this servo pattern S2 corresponds to a length of {fraction (3/2)} of the servo pattern length L3 of the servo pattern S3, the time for STW per track pitch TP is reduced to ⅔ as compared to that of the servo pattern S3.
When the method is used, however, there comes up another problem, although the method has the advantage described above, that large vibrations occur in a magnetic head 1131 when the magnetic head 1131 positions at a dead band described later during data reading, which does not allow the request to be responded to. This is caused by the fact that an angle of yaw made with a center line Xb linking a read core R to a write core W and a tangent line Xa of the cylinder C1 on the magnetic head 1131is set to xcex8 as shown in FIG. 11. Namely, as for the write operation, the write core W always positions at a track center TCxe2x80x2 of the cylinder C1 in the data region RD in data writing shown in the figure, so that a normal write operation is insured.
In contrast, when the read operation is performed, the read core R has to be moved to the side of the cylinder C2 by a correction rate H (Refer to FIG. 11) for displacement of the core as shown in FIG. 13 in order to be positioned at the track center TCxe2x80x2 of the data region RD. During this movement, there comes up a dead band where the read core R can detect only one line of servo pattern S2. More specifically, when the read core R is present at a position B and a position D shown in FIG. 15, the read core R is positioned at the dead bands.
FIG. 16 shows changes of the amplified positional error signal P0 as described above when the read core R is positioned at this dead band. As understood from this figure, when the read core R is positioned at the position B and position D, a voltage V steeply rises in the offset rate OF1 to offset rate OF4 by a voltage displacement rate xcex94V. Accordingly, as this voltage displacement rate xcex94V corresponds to a movement rate of the magnetic head 1131, when the read core R positions at the dead band, the movement rate of the magnetic head 1131 increases, which results in occurrence of vibrations, and in a worst case, the magnetic head 1131 may run away out of control. The influence due to this dead band becomes more significant when the angle xcex8 of yaw shown in FIG. 12 is larger.
It is an object of the present invention to provide, for the purpose of solving the problems as described above, a storage device which can prevent vibrations of a head or the like even when there are a small number of servo patterns for one track on a disk or even when a servo pattern head positions at a dead band and also can reduce a time for STW and a method of detecting a position of the head on a disk used in the storage device.
The storage device according to the present invention comprises a disk having a servo region with a plurality of tracks formed thereon at a prespecified track pitch as well as with m-lines of servo pattern each having a servo pattern length of a 1/m-track pitch for each track formed in time division mode, and a data region for storing therein data. The storage device also comprises a position detecting unit for detecting a position of a head on the disk according to the servo patterns and outputting a result of detection as a detected position signal, and a positional error computing unit for obtaining a positional error between the position detected signal fed-back by the position detecting unit and a positional error signal indicating a target position of the head and outputting a result of computation as a positional error signal. The storage device further comprises an amplifier for amplifying the positional error signal with a prespecified gain and outputting a result of amplification as an amplified positional error signal, and a gain setting unit for setting a gain of the amplifier at the time of data reading to a lower value as compared to a gain at the time of data writing. The storage device also comprises a head moving unit for obtaining an operation rate corresponding to a movement rate of the head according to the amplified positional error signal and moving the head according to this operation rate.
Thus, in the storage device described above, the gain setting unit sets the gain of the amplifier at the time of data reading to a value which is lower as compared to a gain at the time of data writing. When a positional error signal and a position detected signal are inputted into the positional error computing unit it calculates a positional error between the position detected signal and positional error signal and outputs a result of calculation as a positional error signal to the amplifier. The positional error signal is amplified with a gain which is lower than the gain at the time of data writing and is supplied to the head moving unit as an amplified positional error signal. The head moving unit obtains an operation rate corresponding to a movement rate of the head according to this amplified positional error signal and moves the head according to this operation rate.
During this movement of the head, even when the level of the detected position signal steeply rises because the head is located at a dead band where the position detecting unit cannot accurately detect a position of the head, as the gain of the amplifier is set to a lower value, the amplified positional error signal is not directly affected by the steep rise of the level thereof.
Accordingly, with the storage device of the present invention, even when the head is positioned at a dead band the operation rate does not increase, so that vibrations of the head can be prevented and also a number of lines of servo pattern for each track can be reduced, which allows a time for STW in the manufacturing field to be reduced and facilities also to be reduced.
In the present invention, the disk has two lines of servo pattern each having a servo pattern length of a xc2xd track pitch for each track formed thereon in time division mode.
With the storage device of the present invention, two lines of servo patterns each having a servo pattern length of xc2xd of the track pitch for each track are formed on a disk in time division mode, so that the time for STW can be reduced by ⅔ as compared to that in the case where a number of lines of conventional servo pattern is three lines.
In the present invention, the gain setting unit sets a gain of the amplifier at the time of data reading to a value which is xc2xd as compared to a gain at the time of data writing.
With the storage device of the present invention, gain of the amplifier at the time of data reading is set to xc2xd of the gain at the time of data writing by the gain setting unit, so that vibrations generated when the head is positioned at a dead band can be reduced to half as compared to those of the conventional type.
A method of detecting a position of the head on a disk used for the storage device according to the present invention comprises a position detecting step of detecting a position of a head on the disk according to the servo patterns and outputting a result of detection as a detected position signal, and a positional error computing step of obtaining a positional error between the position detected signal fed-back in the position detecting step and a positional error signal indicating a target position for the head and outputting a result of computation as a positional error signal. The method also comprises an amplifying step of amplifying the positional error signal with a prespecified gain and outputting a result of amplification as an amplified positional error signal, and a gain setting step of setting a gain in the amplifying step at the time of data reading to a lower value as compared to a gain at the time of data writing. The method further comprises a head moving step of obtaining an operation rate corresponding to a movement rate of the head according to the amplified positional error signal and moving the head according to this operation rate.
Thus, in the method of the present invention, a gain in the amplifying step at the time of data reading is set to a lower value as compared to a gain at the time of data writing in the gain setting step. In the positional error computing step, a positional error between a position detected signal and a positional error signal are obtained and a result of computation is outputted as a positional error signal. This positional error signal is amplified with a gain lower than that at the time of data writing. Then in the head moving step, an operation rate corresponding to a movement rate of the head is obtained according to the amplified positional error signal and the head is moved according to this operation rate.
During this movement of the head, even when the level of the detected position signal steeply rises because the head is positioned at a dead band where a position of the head can not accurately be detected in the position detecting step, as the gain in the amplifying step is set to a lower value, the amplified positional error signal is not directly affected by the steep rise of the level thereof.
Accordingly, with the method of the present invention, even when the head is positioned at a dead band the operation rate does not increase, so that vibrations of the head can be prevented and also a number of lines of servo pattern for each track can be reduced, which allows a time for STW in the manufacturing field to be reduced by this reduction rate, so that facilities can also be reduced.
In the method of detecting a position of the head on the disk used for the invention described above, the disk has two lines of servo patterns each having a servo pattern length of xc2xd of the track pitch for each track formed thereon in time division mode.
With the method of the present invention, in the gain setting step, a gain in the amplifying step at the time of data reading is set to a value which is xc2xd of the gain at the time of data writing, so that vibrations generated when the head is positioned at a dead band can be reduced to half as compared to those of the conventional type.
In the method of detecting a position of the head on the disk used for the invention described above, in the gain setting step, a gain in the amplifying step at the time of data reading is set to a value which is xc2xd of the gain at the time of data writing.
With the method of the present invention, in the gain setting step, a gain in the amplifying step at the time of data reading is set to a value which is xc2xd of the gain at the time of data writing, so that vibrations generated when the head is positioned at a dead band can be reduced to half as compared to those of the conventional type.
Other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.